Experimental Determination of the Allotropic Transition Temperature Between Tetragonal and Orthorhombic Al 4 Sm Metastable Phases

The allotropic transition temperature associated with the metastable γ -Al 4 Sm (orthorhombic) and β -Al 4 Sm (tetragonal) phases was investigated experimentally. Low-energy X-ray diffraction and differential scanning calorimetry were found to be inconclusive due to the transient nature of the phases involved, which spontaneously decompose to the stable δ -Al 3 Sm and Al-fcc phases. High-energy X-ray diffraction, using synchrotron radiation, however, was able to resolve the transition during continuous heating, enabling detailed analysis of the temperature-dependent diffraction pattern. The γ - β transition temperature was determined to be 896 K, based on a well-resolved transition onset.